The present invention relates to magnetic heads, and more particularly to a magnetic head which is well suited for application to a magnetic recording medium of high coercive force and which has characteristics of high output.
A request for a higher degree of magnetic recording technique, especially for a higher density of magnetic recording, is very eager nowadays.
It is well known that increasing the coercive force H.sub.c of a magnetic recording medium is advantageous for meeting the request. However, a magnetic field having a high intensity and a sharp distribution is needed for recording a signal on a magnetic recording medium of high coercive force. In this regard, in case of using a hitherto-conventional ferrite of high permeability for a magnetic head, the intensity of a recording magnetic field to be attained is limited because the saturation flux density B.sub.s of the ferrite is below 5500 G. This has led to the problem of insufficient recording especially when magnetic tapes of high coercive force being recently developed are employed.
To the end of solving the problem, there has been proposed a magnetic head wherein as shown in FIG. 1, a magnetic metal substance 1 having a high saturation flux density is afforded to the functional gap portion of a head core made of members of the high permeability ferrite 2 and 2', to generate an intense recording magnetic field. Numeral 3 designates a surface facing the magnetic tape. (The details are described in the official gazette of Japanese Patent Application Laid-Open No. 51-140708. Besides, to the end of improving the abrasion-resisting property of a head core, there has been proposed a magnetic head wherein as shown in FIG. 2, the surfaces of the high permeability ferrite members 2 and 2' of the magnetic head core facing the magnetic tape are made of a nonmagnetic substance of excellent abrasion-resisting property 4 (the details are described in the official gazette of Japanese Patent Application Laid-Open No. 58-17522). In FIG. 2, numeral 1 designates a magnetic metal substance. Likewise, a magnetic head has been proposed wherein the surface facing the tape is made of the nonmagnetic substance, a rear magnetic core is made of the high permeability ferrite and the vicinity of a functional gap is made of the magnetic metal substance of high saturation flux density (the details are described in the official gazettes of Japanese Patent Application Laid-Open No. 53-116809 and Japanese Utility Model Registration Application Laid-Open No. 55-93828). It is stated in the official gazette of Japanese Patent Application Laid-Open No. 53-116809 that, since the boundary 5 between the magnetic metal substance 1 and the high permeability ferrite 2 or 2'unpreferably acts as a pseudo gap in the head of FIG. 1, the portion of the surface of the ferrite core facing the tape is made of the nonmagnetic substance as shown in FIG. 2, thereby to bring forth the effect of preventing the pseudo gap from appearing. In the official gazette of Japanese Utility Model Registration Application Laid-Open No. 55-93828, it is stated that the portion of the surface of the ferrite core facing the tape is made of the nonmagnetic substance, which is effective to reduce rubbing noise.
In addition, a magnetic head of a structure in which a pair of magnetic metal members coupled on a nonmagnetic substrate are opposed through a functional gap is described in the official gazettes of Japanese Patent Application Laid-Open No. 59-142716 and European Patent Application Laid-Open No. 0140977.
In general, it can be said that the characteristics of a magnetic head are more excellent as the output C per turn of a coil is higher and as the inductance L per turn of the coil is lower. It is known that the output which can be derived from the magnetic head increases in proportion to the number of turns, and that the inductance of the magnetic head increases in proportion to the square of the number of turns. On account of a requirement for an amplifier circuit, the inductance needs to be suppressed below a certain value determined for each circuit. Accordingly, for the purpose of fabricating a magnetic head exhibitive of a high output with the inductance held below the above value, it is necessary to raise the output per turn to the utmost, namely, to raise the recording and reproducing efficiencies, and besides, to lower the inductance per turn so that the number of turns can be increased within the fixed inductance. In other words, letting L denote the value of the inductance, a higher output C should desirably be obtained for the certain fixed value L or .sqroot.L.
In view of the foregoing, the performance of a magnetic head can be expressed with the ratio C/.sqroot.L between the output C and the square root of the inductance.